New guidelines developed by the United States Centers for Disease Control and Prevention and the American College of Sports Medicine state that significant health benefits can be gained by participating in daily bouts of moderate-intensity physical activity ( et al., 1995). Many of the things people already do, such as brisk walking, heavy housework, or climbing stairs, can produce health benefits if performed for a sufficient duration. Many people, however, think of physical activity and exercise as being different. For many, “exercise” is a vigorous, structured activity performed in a gym or in a class or an activity that requires an exercise machine. On the other hand, overuse of the phrase “physical activity” can mislead people into believing that any activity, including casual strolling or light housework, counts. It is the aim of this chapter to encourage a broad understanding that health benefits can be obtained by both vigorous exercise and moderate-intensity physical activity. In this chapter, therefore, the terms physical activity and exercise are used interchangeably.